Image guide coupler switch

ABSTRACT

In one embodiment, an image guide coupler switch is provided having a dielectric image guide coupler with a coupling control circuit. In this embodiment the coupling control circuit has at least one field pick up probe which extends at least part way across the image guide coupler. A switch is connected in series with the at least one field pick up probe. An optional capacitor my be provided in series with the series with the switch. In some embodiments, a pair of field pick up probes is provided, with the switch being connected in series with and between the pair of field pick up probes. Some embodiments may have multiple pairs of field pick up probes, each having a switch connected in series with a pair of field pick up probes. An optional capacitor may be provided in series with the pair of field pick up probes.

BACKGROUND

At very high frequencies, 30 to 300 GHz for millimeter wave frequencyband, typical integrated circuit transmission lines, such as microstripor coplanar waveguide, become very lossy due to conductor and dielectriclosses, and metal and substrate surface irregularities which can causeunwanted reflections and radiation. At these high frequencies,dielectric waveguides, of which there are a number of different formsprovide a lower loss alternative to signal routing.

Conventional dielectric waveguide switches require a transition from thedielectric waveguide to a transmission line which leads to a localizedswitch circuit. Typical transmission lines have a metal strip on the topside of the circuit substrate and a metal ground on the bottom of thecircuit substrate, or coplanar waveguide which has a signal strip on thetop side of the substrate and two metallic grounds also on the substratetop-side which are separated on each side of the strip by a gap which isdetermined by the desired characteristic impedance of the line. Thesetransitions are typically necessary to connect the image guide tosources, mixers, amplifiers, and switching, but they degrade the overallperformance of the image guide system through parasitic reflections andradiation which increase as the frequency of the system increases.

At very high frequencies, these transitions and transmission lines addRF loss to the overall dielectric waveguide circuit. So, at very highfrequencies, 30 Ghz and up, switches tend to be either very lossy ornarrow band. What is needed is a high frequency switch that providessignal switching without having to remove the signal from the dielectricwaveguide. Also, what is needed is a means to avoid the RF lossesassociated with metallic transmission lines at higher frequencies.Furthermore, what is needed is a device that does not require atransition from dielectric waveguide to printed circuit transmissionline. This is particularly true in high frequency applications.

One alternative approach utilizes an image guide coupler. In thisapproach, a ferrite is placed between the image guides along thecoupling region as disclosed in an article by P. Kwan and C. Vittoria,entitled “Scattering Parameters Measurement of a Nonreciprocal CouplingStructure,” in IEEE Trans. Microwave Theory Technique, Vol. 41, No. 4,April 1993, pp. 652–657. A magnetic field bias applied to the ferritecontrols the coupling between the image lines. Thus, the couplingcoefficient is modified by an external applied magnetic field bias onthe ferrite for isolators, filters, modulators, switches, and phaseshifters. With appropriate external applied magnetic field bias on theferrite, the four port device prior art can be made into an image guideswitch.

With such an approach, however, there are several problems. One problemis that ferrites become lossy at high frequency. What is need is a highfrequency switch capable of providing low loss. Another problem is thatferrites are not easy to integrate into monolithic structures. Thus,there is a need for a switch capable of easy integration into monolithicintegrated circuit structures.

SUMMARY

In one embodiment, an image guide coupler switch is provided having adielectric image guide coupler and a coupling control circuit. In thisembodiment the coupling control circuit has at least one field pick upprobe which extends at least part way across the image guide coupler. Aswitch is connected in series with the at least one field pick up probe.An optional capacitor my be provided in series with the series with theswitch. In some embodiments, a pair of field pick up probes is provided,with the switch being connected in series with and between the pair offield pick up probes. Some embodiments may have multiple pairs of fieldpick up probes, each having a switch connected in series with a pair offield pick up probes. An optional capacitor may be provided in serieswith the pair of field pick up probes.

In another embodiment, an image guide coupler switch is providedincluding a pair of dielectric waveguides adjacent to a metallic ground.The pair of dielectric waveguides have portions in close proximity toeach other so as to allow coupling of electromagnetic signals from oneof the pair of dielectric waveguides to an other of the pair ofdielectric waveguides. A coupling control circuit extends across thepair of dielectric waveguides. In some embodiments, the coupling controlcircuit includes a field pick up probe which extends adjacent at leastone of the dielectric waveguides. A capacitor and a switch are connectedin series with the field pick up probe. The coupling control circuit mayhave a pair of field pick up probes with each field pick up probeextending adjacent a respective one of the dielectric waveguides. Someembodiments may have an array of pairs of field pick up probes, with aseries connected capacitor and switch connected between each pair ofpick up probe.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be betterunderstood with regard to the following description, appended claims,and accompanying drawings where:

FIG. 1 shows a perspective view of an image guide coupler switch inaccordance with one embodiment of the present invention.

FIG. 2 shows an enlarged perspective view of the coupling region of FIG.1 in accordance with one embodiment of the present invention.

FIG. 3 shows a perspective view of an alternate embodiment of thecoupling region of the image guide coupler switch.

FIG. 4 shows an exploded perspective view of the an alternativeembodiment of the image guide coupler switch.

FIGS. 5 and 6 show possible examples of antenna feed structures that mayutilize certain embodiments of the image guide coupler switch of thepresent invention.

DESCRIPTION

FIG. 1 shows a perspective view of an image guide coupler switch 100 inaccordance with one embodiment of the present invention. An image guidecoupler 110 has two waveguides 110 a and 110 b, which may be dielectricrods or bars, located on a ground plane 120. Waveguides 110 a and 110 bcan be machined, molded, or formed by masking, depositing and/or etchingtechniques, depending on the material used and the particularapplication. A number of low-loss dielectric materials exist from whichthe dielectric waveguides 110 a and 110 b can be made. For examplematerials such as Rexolite® (produced by C-Lec Plastics, Inc. ofPhiladelphia, Pa.), Hi-K material (such as produced by Emerson & Cuming,located in Randolf, Mass.), fused silica, Teflon®, ceramics, and evenhigh resistivity semiconductors such as semi-insulating GaAs.

Typically, the image guide coupler 110 is partially surrounded by air soit can support propagating electromagnetic modes. (In the embodiment ofFIG. 1, the metallic ground plane 120 provides a base for the imageguide coupler 110, and a low-loss metallic structure for the lowestorder waveguide mode in the image guide coupler 110. The metallic groundplane 120 may be made from a solid metal slab, or from metal depositedon a semiconductor or insulating substrate.

Since the image guide coupler 110 is not completely surrounded by metal,some of the guided field is located physically outside of waveguide 110a or 110 b, in which it is traveling. The waveguides 110 a and 110 b arebrought into close proximity at a coupling region 115 so that anelectromagnetic field traveling in one waveguide 110 a has some fieldoverlap within the other waveguide 110 b. The result is that energy canbe transferred from one line to the other, over a given interactionlength, as in an image guide coupler. The length of the waveguides 110of the image guide coupler in the coupling region 115 is such thatsignal crosses over at the end of the coupling region 115. Further, theguides are close enough together so the evanescent field, which extendsoutside the one guide, will extend into the other guide. If the guide istoo long the signal will sinusoidally flip-flop. In one embodiment,discussed below, the length of the waveguides 110 a and 110 b areselected so that there is complete cross over coupling from one guide tothe other as a result of the natural evanescent field extending into theadjacent waveguide at the coupling region 115. The separation betweenthe waveguides 110 a and 110 b is increased beyond the coupling region115 so that they do not couple any longer. The strength of the couplingdepends upon the proximity of the waveguides 110 a and 110 b, and howconfined the fields are within the waveguides, i.e. the waveguidematerial and the surrounding medium.

Coupling control circuitry 130 is positioned adjacent to the image guidecoupler 110, and is used to influence the coupling of the image guidecoupler 110. FIG. 2 shows an enlarged perspective view of the couplingregion 115 of FIG. 1 in accordance with one embodiment of the presentinvention. An array of capacitors 150, which may be switched usingswitches 160, are shown straddling the two waveguides 110 a and 110 b.The array of capacitors 150 are shown above the coupling region 115,where the two waveguides 110 a and 110 b are in close proximity. Fieldpick-up probes 170 extend over the two guides 110 a and 110 b. The fieldpick-up probes 170 may be a metal such as copper, or an othertransmissive material.

The capacitor array 150, as well as the field pick-up probes 170, can beconstructed on a very thin (approximately 25 micrometers) layer ofKapton®, which straddles the two waveguides 110 a and 110 b and adheresto the tops of the waveguides 110 a and 110 b. Kapton® is available fromDuPont, of Circleville, Ohio, www.dupont.com. Other printed circuitboard substrates could also be used, but the capacitance values andspacing would need to be tailored for the specific substrate parameters.

The coupling control circuit 130 includes a pair of electric fieldpick-up probes 171 a and 171 b, which are connected to a series circuithaving a capacitor 151 and a switch 161. The capacitor 151 and theswitch may be integrally formed, or be separate structuresinterconnected by a segment 171 c between the capacitor 151 and theswitch 161. The capacitor may be a chip capacitor and the switch 161could be pin a diode, transistor, MEMS switch, etc. Bias lines 142 and143 may be used to actuate the switch 161. The coupling control circuitmay have a single capacitor 151 and switch 161 connected between a pairof field probes 171 a and 171 b. In some embodiments as shown in FIG. 2,the coupling control circuit 130 may have an array of electric fieldpick-up probes 170 a and 170 b. In such an embodiment, all switches 160of the array may be turned on together. To facilitate this, the positivebias lines of each switch can be connected to a common bus line 144,while the negative bias lines can be connected to a common bus line 145.Wires 141 can lead from these bus lines 144 and 145 to respective biascontrol pads 140 which are located away from the image guide coupler, asshown in FIG. 1.

When the switches 160 are not actuated there is an effective opencircuit between the two field pick-up probes 171 a and 171 b. In thiscase coupling between the two waveguides 110 a and 110 b occurs onlyfrom the overlap of the electric field of one waveguide with thedielectric from the other waveguide. When the waveguides 110 a and 110 bare in close proximity, energy is continually transferred from onewaveguide to the other. If the two waveguides 110 a and 110 b haveidentical cross sectional dimensions, at a particular length, known asthe coupling length, all of the signal from the propagating mode of oneguide will transfer completely to the propagating mode of the otherguide. This coupling length depends upon the frequency of the signal,the dielectric constant of the image guide material, and the separationbetween the guides. These factors can be determined from measurements,or from simulation software, such as Ansoft HFSS®, Asoft Corp.,Pittsburg, Pa., www.ansoft.com.

In some embodiments, the cross-over of energy occurs when the switches160 are not actuated, that is when they are open circuited. This isknown as the “cross” state. When the switches are turned on, thecoupling between the two waveguides 110 a and 110 b in the couplingregion 115 is enhanced. The field pick-up probes 170 a and 170 b are nowelectrically connected together, so that RF current can flow between thefield pick-up probes 170 a and 170 b. Thus, current induced in the fieldpick-up probes 170 a and 170 b from the propagating field in one of theimage guides, in turn induces a propagating field in the other imageguide. Most of the field transfer between the image guides still occursfrom the close proximity of the waveguides 110, however, the nowconnected field pick-up probes 170 a and 170 b enhances this coupling bya small amount at each member of the array.

By arranging pick-up probes 170 a and 170 b, switches 160, andcapacitors 150 in an array down the coupling region, enhanced couplingis distributed along the length of the active region 115 image guidecoupler. The amount of coupling is dependent upon the location and shapeof the field pick-up probes 170 a and 170 b and the capacitance of eachswitch and capacitor 150 and 160, and the distance between each switch160 and capacitor 150. For the above embodiment, the effective couplingcoefficient in this case is large enough to allow the RF mode from oneguide cross over to the other guide and then back to the original guidein one cross-over coupling length. This is known as the “bar” state ofthe coupler. Thus, if the two waveguides 110 a and 110 b are identicaland if the coupling region is long enough, energy will couple completelyfrom one guide 110 a to the other 110 b, and then couple back to theoriginal guide 110 a. Again, simulation or measurements can be used todetermine the parameters for this switch/capacitor array. Thus, acoupling control circuit 130 is provided between the “cross” and “bar”states which is controlled by a voltage applied to the array switches160.

When the capacitor array 150 is switched “on”, the coupling is enhanced,which causes the electromagnetic energy to cross into the other guideand then back into the original guide in the coupling length. When thecapacitor array 150 is switched “off” the energy crosses into the otherguide, but does not cross back to the original guide. Thus, the imageguide coupler switch 100 acts as a switch for the electromagnetic wavebetween the two waveguide outputs.

Six switches 160 and capacitors 150 shown are arrayed in FIG. 2,although the exact number required for the switching function to occurmay be determined through simulation and/or experiments. Furthermore,although shown as an array, it is possible in some embodiments toprovide single combined components, i.e. a single capacitor, switch, orpair of probes, if desired. As discussed below, however, one advantagein an array of capacitors 150 and/or switches 160 is that powerdissipation is distributed through the array. In some embodiments (notshown), it is possible to omit the capacitor or array of capacitors 150from the coupling control circuit 130. In such an embodiment, however,the inductance of the field pick-up probes and switch(es) would have tobe low enough for high frequency applications. The capacitor arraydiscussed above, effectively increases the dielectric constant betweenthe two dielectric guides which increases the coupling between the twowaveguides. Thus, some embodiments control of the coupling coefficientis achieved using a switched capacitor array which is located proximateto the two guides. In some embodiments, the capacitor could be a gap, oran array of gaps between the pick-up probes. In certain otherembodiments, the capacitor, or the capacitor array 150 may be completelyomitted from the coupling control circuit 130, with the field pick upprobes 170 being connected via switches 160.

Several embodiments of the present invention allow lower power losses.Because the entire energy of the field is not coupled through thecoupling control circuit 130, losses are reduced. There is little lossin the field pick-up probes, switches and/or capacitors since most ofthe field density remains in the dielectric waveguide. In this respectthe field pick-up probes, the switch and/or capacitor array forms aperturbation to the electromagnetic properties of the image guidecoupler.

The bias lines 142 and 143 may be fabricated small to provide highinductance to ensure that RF energy is not lost in the switch biaslines. The pick-up probes 170 a and 170 b are larger to have lowinductance. The size of the pick-up probes 170 a and 170 is dependent onfrequency of operation.

In alternate embodiments not shown, a high frequency varactor diodescould replace the capacitor and switch combination in the couplingcontrol circuit. Thus a single varactor, or an array of varactors couldbe used.

FIG. 3 shows a perspective view of an alternate embodiment of thecoupling region 315 of the image guide coupler switch 300. In theembodiment shown, the capacitors 350 and the switches 360 contact thewaveguides 310 a and 310 b, respectively. Interconnect segments 355connect the capacitors 350 with the switches 360 across the spaceseparating the waveguides 310 a and 310 b. The interconnect segments 355may be conductor material and function as a field pick up probe. Or, inother embodiments the interconnect segments 355 may be a dielectricmaterial. In yet other embodiments (not shown), the capacitors may beomitted, depending on the application. Not shown in FIG. 3 is theinterconnect circuitry and control logic for the switches 360, as FIG. 3is a simplified illustration for example purposes.

FIG. 4 shows an exploded perspective view of the an alternativeembodiment of the image guide coupler switch 400. In this embodiment,the dielectric waveguides 410 a and 410 b are attached directly on amonolithic circuit 430 which contains the switches 450 and capacitors460. For illustration purposes, the waveguides 410 a and 410 b are shownlifted off the monolithic circuit 430. The back-side 420 of thesubstrate 425 may be metallized. This embodiment facilitates monolithicintegration of other components, such as the RF power source, controllogic, etc. Control logic shown as box 495 may be connected to the biaslines 442 and 443 for controlling the switches 450. The control logic495 may be located on the substrate 425, or remote from the substrate,depending on the particular application.

FIGS. 5 and 6 show possible examples of antenna feed structures that mayutilize certain embodiments of the image guide coupler switch of thepresent invention. Shown in FIG. 5, a switched antenna beam structure500 can radiate a signal in one of a number of directions. The signal isdirected to the appropriate image guide radiator 580, 585, or 590 by aset of coupling control circuits 530 and 531. A receiver, a transmitter,or control circuit chip 597 is shown mounted to the back side of thesubstrate 525 In FIG. 6, a three-bit delay line phase shifter 600 isshown constructed utilizing four coupling control circuits 630–633 toadd or remove delay lines 611 b, 612 b, or 613 b in the waveguide 610 b.A receiver chip 605 is shown adjacent the waveguide 610 a. Although notshown, an RF source may used to launch the fundamental image guidepropagating mode by known adapter techniques. Also, although a pointedradiating element 680 is shown, other types of image guide antennascould be used.

Different embodiments may be constructed for various wavelength signals.Some embodiments can readily be fabricated monolithically as amillimeter wave integrated circuits, as well as for submillimeter waveapplications. Various embodiments may be used in millimeter wave systemssuch as phase shifters, switch networks, or beam steering. Highfrequency imaging and phased array antennas are some examples whichcould incorporate certain embodiments of the image guide coupler forcollision avoidance radar, high resolution seekers, and broadbandcommunication systems. High power applications are also possible as thecoupling circuitry controls the coupling and is not itself handling thefull signal power.

Having described this invention in connection with a number ofembodiments, modification will now certainly suggest itself to thoseskilled in the art. As such, the invention is not limited to thedisclosed embodiments, except as required by the appended claims.

1. An image guide coupler switch comprising: (a) a metallic ground; (b)a pair of dielectric waveguides adjacent the metallic ground, the pairof dielectric waveguides having portions in close proximity to eachother so as to allow coupling of electromagnetic signals from one of thepair of dielectric waveguides to an other of the pair of dielectricwaveguides; and (c) a coupling control circuit extending across the pairof dielectric waveguides, the coupling control circuit comprising: (i)at least one field pick up probe extending adjacent at least one of thedielectric waveguides; (ii) a capacitor connected in series with the atleast one field pick up probe; and (iii) a switch connected in serieswith the capacitor.
 2. The image guide coupler switch of claim 1 whereinthe coupling control circuit comprises a pair of field pick up probes,each field pick up probe of the pair of field pick up probes extendingadjacent a respective one of the dielectric waveguides.
 3. The imageguide coupler switch of claim 2 wherein the coupling control circuitfurther comprises: (a) an array of pairs of field pick up probes; and(b) a series connected capacitor and switch connected between pairs offield pick up probes of the array of field pick up probes.
 4. The imageguide coupler switch of claim 1 wherein the coupling control circuit islocated adjacent a side of the dielectric waveguides opposite themetallic ground.
 5. The image guide coupler switch of claim 1 whereinthe coupling control circuit is located between the metallic ground andthe pair of dielectric waveguides.
 6. The image guide coupler switch ofclaim 1 wherein the pair of dielectric waveguides are located on asubstrate, and wherein the coupling control circuit is located above thepair of dielectric waveguides.
 7. The image guide coupler switch ofclaim 1 wherein the coupling control circuit is located on a substrateand the pair of dielectric waveguides is located over the couplingcontrol circuit.
 8. The image guide coupler switch of claim 1 whereinthe capacitor straddles the area between the dielectric waveguides. 9.The image guide coupler switch of claim 1 wherein the capacitor islocated lateral to the area between the dielectric waveguides.
 10. Animage guide coupler switch comprising: (a) a dielectric image guidecoupler; and (b) a coupling control circuit comprising: (i) at least onefield pick up probe extending at least part way across the image guidecoupler; and (ii) a switch connected in series with the at least onefield pick up probe.
 11. The image guide coupler switch of claim 10further comprising a capacitor connected in series with the switch. 12.The image guide coupler switch of claim 11 wherein the switch and thecapacitor are connected between the at least one field pick up probe anda dielectric waveguide of the dielectric image guide coupler.
 13. Theimage guide coupler switch of claim 12 wherein the capacitor isconnected between the at least one field pick up probe and a firstwaveguide of the dielectric image guide coupler, and wherein the switchis connected between the at least one field pick up probe and a secondwaveguide of the dielectric image guide coupler.
 14. The image guidecoupler switch of claim 11 wherein the at least one field pick up probeis connected between the capacitor and the switch.
 15. The image guidecoupler switch of claim 11 further comprising: (a) an array of fieldpick up probes extending at least part way across the dielectric imageguide coupler; and (b) an array of switches, each switch being seriesconnected with a corresponding field pick up probe of the array of fieldpick up probes.
 16. The image guide coupler switch of claim 15 furthercomprising an array of capacitors, each capacitor of the array ofcapacitors being series connected between a dielectric waveguide of thedielectric image guide coupler and a corresponding field pick up probeof the array of field pick up probes.
 17. The image guide coupler switchof claim 15 further comprising an array of capacitors, each capacitor ofthe array of capacitors being series connected with a correspondingswitch between a corresponding field pick up probe and a dielectricwaveguide of the dielectric image guide coupler.
 18. The image guidecoupler switch of claim 10 wherein the at least one field pick up probecomprises a pair of field pick up probes, and wherein the switch isconnected in series with and between the pair of field pick up probes.19. The image guide coupler switch of claim 10 wherein the couplingcontrol circuit further comprises a plurality of pairs of field pick upprobes, each of the plurality of pairs of field pick up probes comprisesa switch connected in series with respective pairs of field pick upprobes.
 20. The image guide coupler switch of claim 10 wherein thecoupling control circuit further comprises a plurality of pairs of fieldpick up probes, each of the plurality of pairs of field pick up probescomprises a switch and a capacitor connected in series with respectivepairs of field pick up probes.
 21. An image guide coupler switchcomprising: (a) a dielectric image guide coupler, the dielectricwaveguide having a coupling region; and (b) a coupling control circuitconnected adjacent the coupling region so as to be capable ofinfluencing the coupling of the dielectric image guide coupler, thecoupling control circuit comprising: (i) at least one field pick upprobe extending at least part way across the dielectric image guidecoupler; (ii) a capacitor in series with the at least one field pick upprobe; and (iii) a switch connected in series with the capacitor. 22.The image guide coupler switch of claim 21 wherein the coupling controlcircuit comprises a pair of field pick up probes extending across thedielectric image guide coupler.
 23. The image guide coupler switch ofclaim 22 wherein the capacitor is located between the pair of field pickup probes.
 24. The image guide coupler switch of claim 23 wherein theswitch is located between the pair of field pick up probes.
 25. Theimage guide coupler switch of claim 24 further comprising aninterconnect segment between the capacitor and the switch.
 26. The imageguide coupler switch of claim 21 wherein the coupling control circuitcomprises an array of field pick up probes, an array of capacitors, andan array of switches, each field pick up probe of the array beingconnected in series with a corresponding switch of the switch array, anda corresponding capacitor of the capacitor array.
 27. The image guidecoupler switch of claim 26 wherein the array of field pick up probescomprises pairs of field pick up probes extending across the dielectricimage guide coupler.
 28. The image guide coupler switch of claim 27wherein each capacitor of the array of capacitors is located between apair of field pick up probes of the array of field pick up probes. 29.The image guide coupler switch of claim 28 wherein each switch of thearray of switches is located between a pair of field pick up probes ofthe array of field pick up probes.
 30. An image guide coupler switchcomprising: (a) a dielectric image guide coupler, the dielectricwaveguide having a coupling region; and (b) a coupling control circuitconnected across the dielectric image guide coupler, the couplingcontrol circuit comprising: (i) a capacitor; (ii) a switch connected inseries with the capacitor; and (iii) an interconnect segment in serieswith the capacitor and switch, the interconnect segment extending acrossthe coupling region.
 31. The image guide coupler switch of claim 30wherein the switch is connected between one dielectric waveguide of thedielectric image guide coupler and the interconnect segment, and whereinthe capacitor is connected between an other dielectric waveguide of thedielectric image guide coupler and the interconnect segment.
 32. Theimage guide coupler switch of claim 30 wherein the switch and thecapacitor are connected between a dielectric waveguide and theinterconnect segment.
 33. The image guide coupler switch of claim 30wherein the coupling control circuit further comprises an array ofcapacitors, an array of switches, and plurality of interconnectsegments, each capacitor of the array of capacitors being connected inseries with a corresponding switch of the array of switches via aninterconnect segment.